Also known as antibacterials, we are all aware that antibiotics are used to treat infections caused by bacteria. While they help fight infection, they also wipe out "good" intestinal bacteria (healthy microflora) that help keep our digestive systems functioning normally. In the intestines and colon, these microbes help complete the digestive process, and some actually produce vitamins. There's evidence that without normal "good" bacteria in the digestive tract, our immune system wouldn't function properly, and we would be less resistant to harmful bugs. Immediate effects of the disruption of normal gut flora by antibiotics are often diarrhea, cramping, bloating or other unpleasant digestive issues.

Antibiotics are classified by how they work and by the bacteria they act against. Some major classes of antibiotics include:

All of these are considered ‘broad spectrum,’ meaning they treat a variety of bacterial infections. They are also good for treating specific bugs, but often seem to be prescribed with a 'shotgun' mentality, i.e. "We'll just hit whatever's out there." Macrolides and aminoglycosides are commonly prescribed in PCD, especially as more challenging infections begin to emerge. The others are typically used for milder disease in younger children and have fewer side-effects.